In electromagnetic and communications engineering, the term “waveguide” may refer to any linear structure that conveys electromagnetic waves between endpoints thereof. The original and most common meaning is a hollow metal pipe used to carry radio waves. This type of waveguide is used as a transmission line for such purposes as connecting microwave transmitters and receivers to antennas, in equipment such as microwave ovens, radar sets, satellite communications, and microwave radio links.
A dielectric waveguide employs a solid dielectric core rather than a hollow pipe. A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material as they do in a conductor, but only slightly shift from their average equilibrium positions causing dielectric polarization. Because of dielectric polarization, positive charges are displaced toward the field and negative charges shift in the opposite direction. This creates an internal electric field which reduces the overall field within the dielectric itself. If a dielectric is composed of weakly bonded molecules, those molecules not only become polarized, but also reorient so that their symmetry axis aligns to the field. While the term “insulator” implies low electrical conduction, “dielectric” is typically used to describe materials with a high polarizability; which is expressed by a number called the “relative permittivity (∈k).” The term “insulator” is generally used to indicate electrical obstruction while the term “dielectric” is used to indicate the energy storing capacity of the material by means of polarization.
Permittivity is a material property that expresses a measure of the energy storage per unit meter of a material due to electric polarization (J/V2)/(m). Relative permittivity is the factor by which the electric field between the charges is decreased or increased relative to vacuum. Permittivity is typically represented by the Greek letter ∈. Relative permittivity is also commonly known as dielectric constant.
Permeability is the measure of the ability of a material to support the formation of a magnetic field within the material in response to an applied magnetic field. Magnetic permeability is typically represented by the Greek letter μ.
The electromagnetic waves in a metal-pipe waveguide may be imagined as travelling down the guide in a zig-zag path, being repeatedly reflected between opposite walls of the guide. For the particular case of a rectangular waveguide, it is possible to base an exact analysis on this view. Propagation in a dielectric waveguide may be viewed in the same way, with the waves confined to the dielectric by total internal reflection at the surface thereof.
Other features of the present embodiments will be apparent from the accompanying drawings and from the detailed description that follows.